The components of this study include classifying and comparing prevalent streptococcal serotypes causing pyoderma or pharyngitis; characterization of new M-serotypes, determining their importance in these infections; and a systematic investigation of type-specific immunity following streptococcal infections. We seek evidence that immunity against certain pyoderma serotypes of streptococci might result in later immunity for pharyngeal infections caused by strains with a common M-antigen. Cross-reactive immunity following infection by similar or related serotypes is being investigated. The search for new M-antigens is centered upon streptococci agglutinated in the 3/13/B3264 complex, 8/25/Imp.19 and T-11/12; the 3/13/B3264 complex includes many currently prevalent non-M-typable strains. We are also examining relationships between certain M types common to the 8/25/Imp.19 complex, including evidence of cross-reactive immunity in human sera. Sera from patients, catalogued according to age, site of infection, chronological experiences with streptococcal infections, and non-suppurative complications will be systematically examined for type-specific antibody responses by the indirect bactericidal method. The heterogeneity of streptococcal immunity as well as the duration of immunity is being investigated. Humoral antibody, as a mechanism for immunity against streptococcal infections of the skin is not yet well established; we are thus comparing immune responses to that following pharyngitis. Potential value of streptococcal vaccines for the prevention of pyoderma as well as pharyngitis might be better appreciated following these studies. The capability for the young host to mount significant specific immune responses, critical for immune preventive measures, is being documented as a result of studying younger-aged patients with pyoderma. BIBLIOGRAPHIC REFERENCES: Dillon, Hugh C., Derrick, C. Warren and Gooch, Patricia E.: A new M-type of streptococcus pyogenes, group A, of clinical importance in pyoderma and pharyngitis. J. Gen. Microbiol. 91: 119-126, 1975. Derrick, C.W. and Dillon, Hugh C.: Erythromycin therapy for streptococcal pharyngitis. Erythromycin estolate efficacy at a dose of 20 mg/kg/day. Amer. J. Dis. Child. 130: 175-178, 1976.